基于推覆分析方法的支护桩位移监控研究

在已建立基于性能的支护桩测斜监控体系的基础上,在基坑开挖监控过程中引进推覆分析方法。支护桩的性能水平划分为使用良好、明显开裂和倒塌预防3种。将水平测斜数据作为目标广义位移的参考量,用弹塑性方法得到塑性铰属性,使用归一化抽象荷载作用下的弹性地基梁作为支护桩的推覆分析模型,在各施工工况下进行逐步弹塑性推覆分析,以单向单调加载来包络主动区土压力和各种形式的超载,得到支护桩侧向荷载、监测位移、性能水平三者的关系,由当前实测位移反分析支护桩承载性状并估计其继续位移能力,用以开挖监控和加固方案的实施。该方法涉及支护桩破坏过程和位移能力等性能要素,推覆分析方法基于弹性地基杆系有限元方法,推覆荷载归一化为3种可能的模式。最后给出弹性地基梁实现推覆分析的细节和步骤以及一个位于浙江中部软土地区基坑开挖监控的详细算例。实践和算例均表明,该方法结果可靠、简单实用,利于进行基坑排桩结构按变形控制设计和基于性能的开挖监控。

STUDY ON SUPERVISORY CONTROL OF RETAINING PILE DISPLACEMENT BASED ON PUSHOVER ANALYSIS METHOD

After performance-based supervisory control system of retaining pile deformation is established,pushover analysis is introduced into excavation monitoring of deep foundation pit.The performance level of retaining pile is divided into working well(WW),distinct crack(DC) and collapse prevention(CP).Lateral deformation data serve as reference values of target-generalized displacement.Plastic hinge property is obtained by elastoplastic method;and pushover analysis model adopts the beam on elastic foundation under normalized load.Step by step,elastoplastic pushover analysis is carried out under various construction steps;and pushover load increases from unit load to the ones that contain soil pressure in active zone and other load.With this,the relationships among load,lateral deformation and performance level are acquired.So the bearing behavior of retaining pile can be understood;and its succeeding displacement potential under certain real-time lateral displacement can be estimated from inclinometer.This method involves performance factors of materials,including destructive process and displacement capacity of retaining pile.The pushover analysis is based on nonlinear bar system finite element method for beam on elastic foundation.Three conceivable models of soil pressure are normalized to unit load to conduct pushover analysis.Details and processes of pushover analysis are presented in the end,including pushover load,pushover saving step and the termination condition of analysis.An engineering example from a project located in coastal soft soil area shows that the presented method is simple and reliable relatively;and it can be used for performance-based supervisory control of retaining pile deformation.